Dampening fluid



' Addi-liva Oct. 6, 1959 w. s. GLEl-:soN ErAL ,2,907,310

DAMPENING FLUID Filed sept. 1, 1955 will e Unlted States Patent C i ce fwww v Patented Oct. 6, 1959 We have now found that substantiallyimproved results are obtained in hydraulically operated clearance regu-2 907 310 lators by employing, as the hydraulic fluid, amixture of adi-methyl polysiloxane polymer and an ester type plas- DAMPENING FLUID 5ticizer, specifically the compound di-Z-ethylhexyl adipate. William S.Gleeson, Euclid, and 'Edward W. Stevens, Spclflcaul" [.he combmzilogfcgtegsltnghglglsl North Madison, Ohio, assignors to Thompson Ramo p0 ymeravmgoa Vlsfosl .y 1 Wooldridge Inc. a corporation of Ohio at 25 C. (77F.) havmg added thereto at'least 0% by welght, and preferably about 20%`by weight of the .Application September 1, '1955, Serial N0- 532,091 10compound di-2-ethylhexyl adipate produces a more nearly l uniformviscosity characteristic in the temperature range 1 Clam' (CL 12J 90)from about minus 60 to about 300 F. This temperature range includes andindeed exceeds the normal operating temperature range of an internalcombustion engine The present invention deals with improved clearancetappet assembly, regulators, lash adiustors, 0r the like and ndsparticular A further description of the present invention willapplicability t0 ille eld 0f hydraulically Operated aPPeS be made inconjunction with a specic embodiment of the type employed for openingand closing poppet thereof as illustrated in the attached drawings.valves in internal combustion engines. The invention In the drawings; isalso directed to an improved hydraulic iluid C-OmpOSiv Figure l is aview in elevation of a complete tappet tion particularly useful in suchclearance regulators. mechanism employed with an internal combustionengine Automic clearance regulators, of which valve tappetS poppetvalve; and are the best example, are designed to counteract loose-Figure 2 is a longitudinal cross-sectional view ofthe ness or play in amechanical linkage system whether tappet barrel assembly illustrated inFigure l; these irregularities are caused b-y mechanical diliicultiesFigure 3 is a graph comparing leak-down rates with or due to the eiiectsof thermal expansion and contracrespect to temperature between a siliconfluid of the prior tion. In the operation of the regulators, it isimportant art and a dampening tluid according to theV present innot onlythat the clearance regulator be operative to vention. compensate forlooseness in the system, but they must As shown in the drawings; notover control the linkage to produce an undesirable Reference numeral 10indicates generally the tappet tightness, which, in the case ofautomatic tappets, would assembly of the present invention whosemovement is prevent full seating of the valve during operation.controlled by means of a cam 11, supported on a suit- In order tooperate effectively, an automatic tappet able cam shaft 12 of theinternal combustion engine. must have substantially the samecharacteristics, regard- The vertical movement of the elements in thetappet less of the temperature at which it is employed; Thus assembly 10is transmitted to a poppet valve 13 in the the tappet must be readilyoperable under low temperaengine block by acting on'the tip 14 of thevalve stem ture conditions encountered when starting the engine in 13a.A spring retainer 15 is locked on the valve stem cold weather and shouldoperate eifectively, without sub- 13a to bottom a valve spring 16surrounding the valve stantial change of characteristics, even under thehigh stem and compressed between the retainer 15 and thev temperatureconditions encountered after prolonged use 40 engine block. in a highspeed engine. Thetappet mechanism itself includes a cylindrical To alarge extent, the response characteristics of a barrel 17 having an opentop and the closed bottom indihydraulically operated tappet aredependent upon the cated at 17a. A relatively light, cylindrical coiledspring type of hydraulic fluid contained within the unit. It is 18 isdisposed at the base of the hollow cylinder 17 and particularlyimportant that the uid employed have a exerts a relatively light forceon a choke ring 19 which reasonably constant viscosity characteristicalong an exhas `a smaller outer diameter than the inner diameter oftended range of temperatlues. This characteristic is dethe barrel 17.The choke ring 19 prefelably has a gensirable in the hydraulic iluid,but is rarely achieved. For crally triangular cross-section so that itprovides an inner example, a typical hydraulic fluid presently beingemtapering valve seating face 19a along its inner surface. ployed intappets has a viscosity of `about 950 centistokes Also included withinthe barrel 17 is an elastomeric at a temperature of about 40 F., butthis viscosity falls synethetic rubber cup seal member 21 which engagesto a value of less than 200 as the temperature is raised the walls ofthe barrel 17. The rubber cup member 21 to 200 F; As a result, theoperation in the hydraulic has a central bore therethrough whichreceives the shank tappet may be sluggish at low temperatures orexcessively 22a of a valve member 22. The Valve member 22 also fast athigh temperatures. has an enlarged head portion formed with a valveseat- We have now found that the viscosity characteristics ingtsurface22h which is arranged to become seated of the hydraulic fluid can bestabilized, where the fluid in the valve seat surface 19a of the chokering 19. is a polysiloxane polymer, by the addition thereto of cer- Theshank 22a of the valve member 22 is also slidably tain ester typeplasticizers and that when such mixtures received within a lower plungermember 24 having an are used in hydraulic tappets, the leak-downtime ofthe enlarged annular flange portion 24a bottomed against tappet becomespractically constant, at constant load, the upper surface of the rubbercup member 21. irrespective of temperature. An upper plunger member 26is press fitted or other- Accordingly, an object of the presentinvention is to wise secured to the top end of the shank 22. The upperprovide an improved hydraulically controlled clearance plunger member 26has a relieved portion 26a which reregulator whose operationalcharacteristics are not varied 55 ceives an elastomeric sealing ringsuch as a synthetic substantially by extreme changes in temperature.rubber circular seal 28 in sealing relation against the Another objectof the invention is to provide a hysurfaces of the barrel 17 so `as toprevent dirt and other draulically operated, automatic tappet' forinternal comcontaminants from entering the interior of the tappetbustion engines with an improved type of hydraulic fluid. mechanism.

Still another object of the invention is to provide an improvedhydraulic fluid having general utility in various elds of application.

The upper plunger member 26 is also provided with a relieved shoulderportion 26h which serves to provide a means for containing a helicalreturn spring 27 which normally separates the upper plunger member 26from the llower plunger member 24. The spring 27 is preferably heavierand stiier than the spring 18.

In accordance with the present invention, the bottom portion of thetappet barrel 17, up to the upper cup member 21 is filled with a'hydraulic uid 25 comprising prferably a vmixture of a methylpolysiloxane polymer having a viscosity in the range from about 100,000to about 1,000,000 centistokes at 25 C., having dissolved therein from lto 50% by weight and preferably about by weight of the compounddi-2-ethylhexyl adipate.

The choke ring 19 and the valve head 22h divide the lower portion of thetappet assembly into a lower pressure compartment A and a storagecompartment B about the level of the valve and its valve seat. Thereturn spring 27 bottoms the cup member 2l against the fluid in thecompartment B.

In the operation of the tappet mechanism, when the cam 11 is in aposition for moving the tappet 10, the load of the valve spring 16 istransmitted to the valve member 22 and through this valve member 22 tothe choke ring 19. Since the choke ring rests on the body of hydrauliciluid 25 in the compartment A, the lifting pressure from the tappetbarrel will be transmitted through the trapped oil in compartment A tothe valve member 22 and finally to the engine valve 13. Some leak-downoccurs between the outer periphery of the choke ring 19 and the innerwall of the barrel 17 thereby causing the hydraulic fluid to flow =fromcompartment A to the storage compartment B. As this leak-down occurs,the tappet valve 22 drops in the barrel, thereby shortening theassembly.

When the cam 11 has moved to a position in which it no longer applies avalve opening load on the valve spring 16, the tappet return spring 27takes over and expands to force the upper plunger 26 upwardly throughthe open end of the barrel 17. As this occurs, the valve seating face22b of the valve element 22 becomes unseated with respect to the valveseating face 19a of the choke ring 19. As the valve element'is opened,the cornpartment A is placed in full fluid communication with thestorage compartment B. At the same time, the duid in the compartment Bis under the compressive force exerted by the expanding return spring 27through the lower plunger member 24 and the cup member 21, therebyforcing iluid from compartment B to compartment A. A condition ofpressure equilibrium is promptly reached between the two compartments,and the valve seating face 22h will be seated, or very nearly seated,upon the valve seating face 19a of the choke ring 19.

Tests have indicated that the use of the improved hydraulic fluid of thepresent invention provides a substantially constant leak-down rate, atconstant load, over a wide range of temperatures. In thischaracteristic, the duid differs very radically from the same siloxanepolymer when employed in the absence of the diester additive. Forexample, it was 'found that at a temperature of about 0 F., a tappetassembly employing a polymer without the additive required a leak-downtime of about 300 seconds at a given load. The same polysiloxane fluidcontaining 20% by weight of di-Z-ethylhexyl adipate required a leak-downrate of only about l5 seconds at 0 F. At increases in temperature, thesiloxane polymer containing no additive exhibited a very rapid decreasein the leak-down time required, and at a temperature of about 250 F.,the leak-down time had been reduced to about 20 seconds. In contrast,the leak-down time for the iluid containing the additive was fairlyconstant from a temperature of minus 30 to 300 F., and never exceededaboutseconds, nor fell below 10 seconds.

The results of the tests described above are depicted in graphical formin Figure 3 of the drawings, wherein the curve labelled silicone fluidwith 20% additive demonstrates how the fluid of the present inventioneX- hibits substantially constant leak-down characteristics throughout anormal operating range of temperature.

Additional tests also indicated clearly that the iluid.

containing the diester additive possesses a viscosity Lstabilityrbothstatically and dynamically under load which is not present in the uidwithout the additive.

The improved behaviour of the fluid under widely varying temperatureconditions indicates that the Huid may be employed not only in clearanceregulators, but

also in other systems where such characteristics are desirable.Speciiically the uid may b'e employed in lhydraulic systems ofhydraulically operated brakes lo'w temperature hydraulic systems, anddamping 'or dash p'o'rt type mechanisms.

It should be evident that various modilications can be made to thedescribed embodiments without departing from the scope of the presentinvention.

We claim as our invention:

An automatic clearance regulator for an internal com-v bustion enginecomprising first and second relatively movable parts togethery forming afluid reservoir and having a leak-down passage through which dampeningfluid in said reservoir is forced upon relative movement of said firstand second parts, and a dampenin'g fluid in said reservoir comprising adi-methyl polysiloxane polymer having a viscosity of at least about100,000 centi- Stokes at 25 C. and having added thereto in amount of 10%to 50% by Weight the compound di-2-ethylheXyl adipate and said dampeningfluid exhibiting substantially constant leak-down characteristics in atemperature range in the order of from about 30 F. to +300 F.

References Cited in the file of this patent UNITED STATES PATENTS2,570,853 Pierce Oct. 9, 1951 2,570,854 Pierce Oct. 9, 1951 2,583,604Sirianni et al. Ian. 29, 1952 2,642,395 Currie lune 16, 1953 2,684,336Moreton July 20, 1954 2,698,837 Gamrath et al. Jan. 4, 19'55 2,742,030Gleeson Apr. 17, 1956 2,742,031 Tauschek Apr. 17, 1956 FOREIGN PATENTS502,064 Belgium Apr. 14, 1951

